Vent system for liquid molding

ABSTRACT

A closed injection mold for molding liquid resins into molded plastic articles containing at least one vent apparatus having a reciprocating vent pin operative to retract to open the vent opening and extend to close the vent opening. Each vent apparatus is responsive to a full resin level in the mold cavity to close the vent opening. When the vent opening is closed, cleansing fluid is automatically circulated through the debris charge line of the vent apparatus to clear the venting channels prior to the resin debris hardening.

This is a division of application Ser. No. 08/102,169, filed on Aug. 4,1993, of James K. Brew, for "VENT APPARATUS AND SYSTEM FOR LIQUIDMOLDING" now U.S. Pat. No. 5,397,230.

TECHNICAL FIELD

This invention relates to a vent apparatus and system for molding andparticularly to a venting unit for liquid molding processes such asstructural reaction injection molding (SRIM), resin transfer molding(RTM), and reaction injection molding (RIM).

BACKGROUND

Liquid molding processes require molding resins to be injected into aclosed mold in a liquid state where the liquid resins are hardened intoa molded plastic article. During the injecting step, air in the mold isdisplaced and forced out of the mold cavity through vents. The displacedair is ordinarily vented to the exterior of the closed mold. If air isnot permitted to escape or otherwise ventilate from the mold cavity, thenon-ventilated air will inhibit resin flow within the mold cavity,become entrained in the fluid resin, and remain trapped within themolded article, possibly causing a defective or scrap molded article.

Prior systems for venting closed molds ordinarily consist of channelscut into the mold through the tool parting line, or hoses from ventsprues, or the air is simply allowed to bleed out under pressure throughthe perimeter seal of the mold.

The prior art processes, however, frequently release displaced gases andwaste material into the environment. Further operating problems includethe inability to accurately and consistently control filling of the moldcavity as well as the inability to build constant pressure in the moldcavity due to uncontrolled open ventilation. Also, the prior art ventingapparatus generally do not include self-contained cleaning meansoperative to clean the mold means of resin or other waste debris afterthe vent is closed.

SUMMARY OF THE INVENTION

A closed injection mold for molding liquid resin is fitted with at leastone vent apparatus for expelling air displaced from within the closedmold during the resin injection process. The vent apparatus comprises aventing tube or nozzle communicating with a vent opening in the moldwhere the venting tube is fitted with a reciprocating closure meansadapted to close the vent opening in response to complete filling of themold cavity with liquid resin. The vent apparatus also comprises a purgechannel containing an entrance channel and a debris discharge channel,both of which are interconnected to the vent tube. During the moldingcycle and while the vent opening is closed, the entrance purge channeltransports cleansing fluid, such as air or organic solvent, to entrancepurge the debris discharge channel of resin particles and other debrisexpelled from the mold cavity during charging of the liquid resin to themold cavity.

In accordance with the process of the present invention, liquid resin isinjected into the closed mold cavity while the reciprocating closuremeans is retracted and the vent tube is maintained opened. This permitsair displaced from the mold cavity during resin filling of the mold tovent freely through the vent tube and exit to the atmosphere through aresin discharge channel. Upon complete filling of the mold cavity withliquid molding resin, the reciprocating closure means is extended toclose the vent opening. A plurality of vents can be independentlyoperated and sequenced to close in order to achieve complete and properfilling of the mold cavity. Closing of the vents permits internal cavitypressure to build up as desired. Meanwhile, upon closing of the ventopenings, cleansing fluid is caused to circulate through the entrancepurge channel and the debris discharge channel to flush the ventingapparatus of resin particles and other debris, which is particularlyadvantageous and important when thermosetting liquid molding resins areused. The venting apparatus of this invention advantageously operatesindependently of closing the mold and mold internal pressure, andpreferably is positioned in line with the resin material flow within themold cavity. The self-contained, self-cleaning venting apparatus can bemanually or automatically activated during the molding cycle inpreparation for the next resin injection filling cycle. The ventingapparatus is particularly useful with the molding of thermosettingliquid resin such as polyesters, vinyl or acrylic esters, ethylenicallyunsaturated resins, urethanes, epoxy resins, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front elevation view of the vent apparatus of the presentinvention shown partially in section to better illustrate the vent in aclosed vent position;

FIG. 2 is a view similar to FIG. 1 but showing the vent apparatus in anopen position;

FIG. 3 is a sectional view taken along lines 3--3 of FIG. 2;

FIG. 4 is a schematic of a process controller system for automaticallyactivating various operating parts of the vent apparatus of thisinvention shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and more particularly to FIG. 1, a ventingapparatus 10 is shown operatively interconnected to a vent opening 12 inclosed mold 14, which is particularly useful for liquid injectionmolding of plastic articles within mold cavity 16.

Venting apparatus 10 comprises a hollow vent tube or nozzle 20 having aninterior vent channel 22 with a bore diameter essentially the same asthe bore diameter of the vent opening 12 in the closed mold 14. Theinterior vent channel 22 is adapted to slidably engage a reciprocatingvent pin 24 operative to extend downwardly as shown in FIG. 1 to closethe vent opening 12 and operative to retract upwardly as shown in FIG. 2to open the vent opening 12. The reciprocating vent pin 24 essentiallyhas the same diameter as the vent channel and is operativelyinterconnected to a reciprocating actuating means such as a pneumaticcylinder 26. Hence, reciprocating movement of the vent pin 24 isoperative to open the vent opening 12 to vent the mold cavity ofdisplaced air during the liquid resin charging of the mold cavity 16 andsubsequently close the vent opening 12 to maintain the liquid resinwithin the mold cavity 16 during the molding cycle.

Vent channel 20 can be secured to the mold 14 at the parting line 18(exterior mold surface), as shown in FIGS. 1 and 2, which produces asprue on the molded part that remains with the molded part when removedfrom the mold. Alternatively, the nozzle 20 can be inserted through themold wall 14 and be flush with the interior wall, not shown.

Referring now to FIGS. 1 and 2, the upwardly extending vent tube 20 isconnected to a purging channel 27 communicating with the vent channel22. The purging channel 27 has an input opening 30, an entrance channel28, and a discharge opening 32 where channel section 29 also serves as amold and debris discharge port. Debris discharge channel 29 cangenerally be horizontal, as shown, or have a vertical leg such that itis symmetrical to the input opening 30 and entrance channel 28. Thepurging channel 27 is interconnected with a hollow feed hose 34 which inturn is interconnected with a selector valve 36 operative to permit air40 under pressure and/or organic solvent 42 to flow into the purgingchannel 27. Valve 36 can be closed completely to exclude solvent 42 andair 40 from entering the purging channel and also to close input opening30 to prevent flow of material discharged from the mold to flow throughentrance channel 28, but rather the same is forced out discharge opening32. The air which is discharged from the mold will contain some debris,i.e., resin, which is deposited in the discharge channel 29, especiallyduring the terminal portion of the mold charging cycle. The cleansingfluid, when utilized, will remove the deposited debris from purgechannel 27. The fluid cleansing means is shown in FIG. 1 for clarity andit is understood that the purging and cleansing of the purge channel 27occurs while the vent pin 24 is extended and the vent opening 12 isclosed as shown in FIG. 1. Sectional means shown in FIG. 3 furtherillustrate the purging channel 27 where the vent pin 24 is retracted inthe open position as shown in FIG. 2. As apparent from FIGS. 1 and 3, alongitudinal diameter 31 of the purge channel in the vicinity of ventpin is greater than the diameter of vent pin 24 thereby permitting air40 and/or solvent 42 to flow into entrance channel 28, around vent pin24, and through debris discharge channel 29. Vent apparatus 10 also hasa cooling jacket therein.

FIG. 4 shows a process controller 50 having an electrical lead 52connected to an electronic resin sensor 54 adapted to measure the liquidresin level within the mold cavity 16 where excess charged liquid resinenters through the vent opening 12 and commences entry into the ventchannel 22 thereby activating the process controller 50 to shut the ventopening 12. The electronic signal sent to the process controller 50 inturn activates the reciprocating means through lead line 56 to anelectronic activating means 58 for actuating the reciprocating means andextending the movement of the vent pin 24 to close the vent opening 12as shown in FIG. 1. The process controller is then programmed to openthe valve 36 by controller lead line 60 and activating means 62 inconjunction with activating the air source 40 or the organic cleaningsolvent source 42. Process controller lead line 64 activates the airsource 40 while controller lead line 66 activates the organic solventwhere either cleansing fluid can be used alone or in programmedsequence, or together, if desired, to clean resin particles and otherdebris from the discharge channel section 29. The purging process of thedischarge channel section 29 takes place while the vent opening 12 isclosed and liquid resin in the mold cavity 16 is hardened into a moldedplastic article. After the molding cycle is completed, the mold halvesare separated and the molded part is removed while the processcontroller 50 automatically reverses movement of the reciprocating meansto retract the vent pin 24 and open the vent opening 12 in preparationfor liquid resin injection into the mold cavity 16 in a subsequentmolding cycle.

In accordance with the process of this invention, displaced air isvented from the closed mold 14 by controlling air expulsion with areciprocating vent apparatus 24 retracted to the open position whilecharging liquid resin to the mold cavity 16; automatically sensing theliquid resin level within the mold cavity 16, and automatically closingthe vent opening 12 in response to the liquid resin entering the ventopening 12 by extending the reciprocating vent pin 24; and purging thevent apparatus of debris by automatically activating passage ofcleansing fluid through the debris discharge channel 29 while the ventopening 12 remains closed, as shown in FIG. 1.

In lieu of the above described automatic system, other automatic systemscan be utilized as well as semiautomatic, and even manual systems, foractivating the reciprocating vent pin, the selector valve, and the like.

One or more vent units of this invention can be used on a single closedmold where a plurality of vents can be operated, e.g., closed, in apredetermined sequence or each independently in response to individualresin sensors for each vent opening 12. Air in the mold is effectivelydisplaced and completely forced out through the vent units therebyproducing defect-free molded articles. The process controller 50 can beprogrammed to automatically close all vent openings 12 at an appropriatetime so that a suitable internal cavity pressure can be developed, or sothat no pressure exists. The plurality of vents can be sequentiallyopening and closed in some predetermined manner in order to achieveproper and complete filling of the mold cavity 16. As noted, after thevent openings 12 are closed, the process controller activates fluidcleansing of the debris discharge channel 29. Cleansing advantageouslyflushes out resin particles and other debris before the resin is allowedto cure or otherwise harden and set-up within the debris dischargechannel 28.

While in accordance with the patent statutes the best mode and preferredembodiment has been set forth, the scope of the invention is not limitedthereto, but rather by the scope of the attached claims.

What is claimed is:
 1. A process for injection molding liquid resin in aclosed mold cavity, the mold having at least one vent opening forexpelling air from the mold cavity during the filling of the mold cavitywith liquid resin, comprising the steps of:controlling the air expulsionwith a venting means comprising a vent tube interconnected with the ventopening in the mold, the vent tube communicating with a debris dischargechannel, the vent tube fitted with a reciprocating vent pin operative toextend to close the opening in the mold and to retract to open theopening in the mold; filling the mold cavity with liquid resin whilemaintaining the vent pin retracted to permit displaced air to vent fromthe mold cavity; controlling the reciprocating vent pin in response tothe liquid resin level in the mold cavity to extend and close the ventopening in the mold; and purging the venting means with cleansing fluidto clear the venting means of debris.
 2. A process according to claim 1,wherein the venting means contains a purging channel communicating withthe vent tube whereby cleansing fluid is passed through the purgingchannel to clean the debris discharge channel.
 3. A process according toclaim 1, wherein the venting means is controlled by sensing the resinlevel within the mold with a resin level sensor operative to extend thevent pin and close the vent opening in the mold in response to liquidresin entering the vent opening.
 4. A process according to claim 2,wherein the venting means is purged with fluid comprising air.
 5. Aprocess according to claim 2, wherein the venting means is purged withfluid comprising organic solvent.
 6. A process according to claim 2,wherein the venting means includes a process controller where theprocess controller automatically activates the cleansing fluidcirculation when the vent pin extends and closes the vent opening in themold.